Disposable transducer seal

ABSTRACT

A disposable transducer seal designed to seal an open aperture of a transducer housing for a therapeutic ultrasound procedure. The seal has a membrane, a retainer and a mating device for locking in place with the transducer housing. The membrane is essentially transparent to ultrasound energy while being stretched taunt about the retainer.

CROSS-REFERENCES TO RELATED APPLICATIONS

The subject matter of the present application is related to that of thefollowing applications each of which is being filed on the same day asthe present application: U.S. Ser. No. ______, entitled “Medical DeviceInline Degasser” (Attorney Docket No. 02356-000500US); U.S. Ser. No.______, entitled “Articulating Arm for Medical Procedures” (AttorneyDocket No. 02356-000600US); U.S. Ser. No. ______, entitled “Acoustic Gelwith Dopant” (Attorney Docket No. 02356-000800US); ______, entitled“Position Tracking Device” (Attorney Docket No. 021356-000900US);______, entitled “Ultrasound Therapy with Hood Movement Control”(Attorney Docket No. 021356-001100US); ______, entitled “Systems andMethods for the Destruction of Adipose Tissue” (Attorney Docket No.021356-001200US); ______, entitled “Component Ultrasound Transducer”(Attorney Docket No. 021356-001300US); the full disclosure of each ofthese applications are incorporated herein by reference.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH AND DEVELOPMENT

NOT APPLICABLE

REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAMLISTING APPENDIX SUBMITTED ON A COMPACT DISK.

NOT APPLICABLE

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to a sealing device for retainingdegassed water within an ultrasound transducer housing.

BRIEF SUMMARY OF THE INVENTION

2. Description of the Prior Art

Ultrasound transducers require a coupling medium to connect thetransducer to a patient in order to prevent the reflection andrefraction of ultrasound waves when those waves cross a border betweendensities of two objects. One of the biggest issues in couplingtransducers to a patient either for a diagnostic ultrasound device, or atherapeutic ultrasound device, is the presence of air. Coupling agentsare used to eliminate large scale air bubbles between the transducer andthe patient. For diagnostic purposes, mineral oils, hydro-gels and evenwater can be used to couple a transducer to a patient. In therapeuticprocedures the coupling agent should be more strictly controlled so thateven minute air bubbles are eliminated.

In high intensity focused ultrasound (HIFU) procedures the need tocouple the transducer to the patient often includes a means of coolingthe face of the transducer, or cooling a patient's skin, with a mediumthat will pass ultrasound energy with little or no attenuation oradverse effect. Typically this medium is water held within atransmission cavity with a cap or membrane, and through which theultrasound energy passes.

One major issue with such a system arises from bubble formation causedby dissolved gasses being drawn out of solution. These bubbles providean impedance mismatch to the ultrasound energy, causing reflections andlocalized heating, leading to observed effects such as reducedeffectiveness of therapy, the destruction of the cap or seal, or patientskin burns.

Atmospheric water for example, contain approximately 8.5 PPM (parts permillion) O₂, and 14.5 PPM N₂ as well as other dissolved gasses. Usingdissolved oxygen (DO) as an indicator (by partial pressures the relativecontents of other gasses, CO₂, CO, N₂, etc. . . . can be calculated) itis necessary to reduce the DO to less than 5 PPM in order to reduce theattenuation effects to a manageable level.

The common method used by the industry is to prepare the fluid bypassing it through a filtration and de-ionisation process to removeimpurities and particulates that may precipitate out, contaminate orprovide nucleation sites for bubbles. The coupling fluid is thendegassed to some minimum level before introduced into the system.Typically degassing is performed by bulk cavitation under a vacuum orboiling at atmospheric or sub atmospheric pressure and then sealing thedegassed fluid in a container.

In a completely sealed system the dissolved gas content will remainconstant, but as described below the gas content will strive to meetequilibrium with the partial pressure of the local atmosphericconditions. During short procedures or low power ultrasound proceduresthe re-gas rate is usually slow enough not to cause problems. In longerprocedures and/or at higher powers, the probability that re-dissolvedgas will be drawn into the fluid, and subsequently interfere withultrasound transmission, goes up considerably since it is impossible toprevent gas diffusing through the system lining, joints and sealswithout investing in prohibitively expensive parts and materials.

The methods by which gasses come out of solution or enter the coolingsystem are various, some examples of the more common range from pressurechanges within the cooling system caused by physical restriction oratmospheric conditions. Local pressure changes such as rectifieddiffusion from HIFU or temperature changes will bring gas out ofsolution as will displacement of the partial pressure of one gas byanother, or by material leaching. Other methods by which gas may enterthe system include diffusion through the tubing, seals and structure ofthe cooling system in the same way a balloon deflates, trapping microbubbles within the surface structure and pockets of the cooling system,chemical reactions between materials in the cooling system, or as a byproduct of bacterial growth within the cooling system.

Precautions such as using low permeability materials for the tubing areregularly employed, but even with such precautions, the re-gas rate canbecome a major issue. Other methods used to reduce the effects ofre-gassing include the introduction of surfactants or wetting agents toprevent bubble formation, using larger volumes of fluids, and the use ofhydrophilic and/or hydrophobic polymers such as Polyvinaylpyyolidone(PVP). Experimental testing has shown these provide only a short termsolution.

Numerous examples in the prior art show differing solutions to theproblems of dealing with coupling HIFU transducers to a patient as wellas providing an apparatus for degassing a fluid. However there has beenthus far nothing demonstrating the feasibility or utility of an in linedegassing mechanism combined with a HIFU therapy system during an actualmedical procedure or application. The use of an inline degasser during aprocedure mandates the use of a transducer housing having a cavity wherethe cooling/coupling fluid may circulate around the transducer. Toprevent the coupling fluid from escaping the cavity, a seal is needed.

The inability of the prior art to maintain a controlled dissolved gascontent in a cooling fluid over a prolonged procedure acts as a forcedlimitation to prolonged HIFU therapy.

Thus there remains a need for a seal capable of retaining a degassedcoupling fluid for use in a HIFU procedure within a cavity containing aHIFU transducer.

BRIEF DESCRIPTION OF THE DRAWINGS

It is an objective of the present invention to provide for a seal thatis both inexpensive to manufacture, and that can be quickly and easilyinstalled into a transducer housing.

It is a further object of the invention to make a seal that isdisposable so reuse and sterility issues need not be an issue.

These objectives are provided for in a disposable transducer seal thatcomprises a membrane that is substantially transparent to ultrasoundenergy. The membrane is non-porous to water and acoustic couplingfluids. A retainer has an annular configuration. There is also a meansto mate the retainer with a transducer housing.

DETAILED DESCRIPTION OF THE INVENTION

The device of the present invention is a disposable transducer seal(seal). The seal is designed for use with a system for the reduction inadipose tissue. The seal comprises a membrane, a retainer and a meansfor attaching the seal to a transducer housing. The transducer housingis shaped similar to an inverted cup having a gap space for degassedwater. The seal is used to retain the degassed water in the gap spacewithout the water spilling onto a patient during an ultrasoundprocedure. The seal is intended to provide both an air tight seal, and abarrier to prevent cross contamination of the different fluids onopposite sides of the membrane.

The membrane is composed of a compound being essentially orsubstantially transparent to ultrasound energy. The membrane may becomposed of naturally occurring materials such as latex rubber, or asynthetic material like a thin film plastic or rubber. Thermoformingplastics produce good membranes since the thickness of the membranetends to be uniform. Uniformity in the membrane of the seal reducesscattering of the ultrasound signal during a procedure. A thermoformingpolyimide provides a good example. For manufacturing considerations andfor optimal performance, the synthetic polyimide is preferred. Themembrane may be flexible or inflexible as long as it is drawn tauntabout the retainer. While the membrane may be inflexible, it ispreferred the membrane be a little flexible so that it can conform tothe curves of a patients body more readily. Some flexibility also allowsthe membrane to respond to fluid pressure changes during procedures.This responsiveness during a procedure helps maintain a constantpressure environment for the fluid, since the membrane may expand alittle or contract a little due to variations in pressure in the system.The membrane serves as an acoustic window, so it is desirable that themembrane is substantially transparent to ultrasound energy. Smoothnessin its surfaces during manufacturing will help reduce signal scatteringor attenuation, thus improving performance of the membrane. A plasticmembrane having desirable acoustic properties is required, and if thatplastic is thermo-formable it allows for a greater uniform thickness inthe manufacturing of the membrane. Uniform thickness also helps toreduce signal scattering or other loss of the ultrasound signal passingthrough the membrane.

The retainer may be assembled from any medically approved material.However since the retainer may be in direct contact with the patient, itis preferred to be made of a material that is easily formable (such asan extruded plastic, or moldable plastic) so that the sealing device maybe discarded after a single use. The membrane is drawn taunt over theretainer, or drawn taunt and the retainer is placed down about themembrane so that the membrane remains taunt during a medical procedure.

The seal has a means for mating with a transducer housing. The means maybe such as the retainer is shaped as an interlocking ring with thetransducer housing having a conforming receiving aperture. Or thetransducer housing may have clips for latching on to tabs on theretainer. Other means of mating to the transducer include a magneticlock, a screw in pin, a temporary adhesive, an interference fitting maleand female part (one being on the retainer, the corresponding part onthe transducer housing).

The retainer may also include a means for identifying the sealing deviceto the transducer housing, or its attached ultrasound system. The meansmay be an electronic device such as an encoded chip or flex circuit, orit may be linked to the mating means, such that if the mating is notproperly done the transducer housing and corresponding ultrasound systemwill not recognize the retainer and therefore remain in a safe mode.

Either the membrane or the retainer may also have a clear window. Thewindow is a small gap space designed to correspond to the location of anoptical emitter and photo-optical receiver such that an acoustic gelhaving a safety dopant can be detected by the transducer housing orultrasound system through the sealing device.

Referring now to the drawings, FIG. 1 illustrates several possibledesigns. The retainer 592 of the disposable transducer seal 590 has anannular configuration. The membrane 594 is drawn tightly around theretainer 592. Regardless of the material construction of the membrane,it is necessary for the membrane to be drawn tightly about the retainerand held in place. Thus if the membrane is a polymer formed into a thinlayer, or a softer latex rubber, the retainer serves to maintain theshape and rigidity of the membrane during use. If the membrane is asofter material, such as a latex rubber, then the retainer serves tokeep the membrane taunt. Preferably the membrane has no slack in it, sothere is no play or deformation of the membrane during use. A limitedamount of deformity is desirable so the membrane can flex slightly to beconcave or convex relative to the transducer. However ripples in themembrane material, folds or even a somewhat flimsy shape to the membranemay have adverse effects on the transmission of ultrasound energy duringa procedure. The configuration is a circular ring, square, rectangle orother loop as required to seal a transducer housing. Thus the annularconfiguration depends on the aperture of the transducer housing the sealmust mate with. The precise shape will vary from one transducer housingto another. The shapes shown are merely illustrative and not to be takenas limiting in any sense.

FIG. 2 illustrates a cross section of the sealing device. As can be seenthe membrane is drawn tightly either within the retainer (FIG. 2A) oracross the surface face of the retainer (2B). Optional elements includethe encoder chip 596 illustrated in both drawings.

FIG. 3 illustrates the mating of the seal 590 to a transducer housing500. The housing is shaped similar to an inverted cup containing anelectronics and motor assembly for moving and controlling the transducerand any additional electronic components that may be integrated into thehousing. The seal 590 is placed over an open aperture on the transducerhousing. The design of the transducer housing is such that thetransducer is placed aperture end toward the patient, and the transducercan abut the skin of the patient. The transducer housing may be used intwo modes. One of those modes involves the use of degassed watercirculating about the transducer within the transducer housing. A sealis needed in this mode of operation to prevent the degassed water fromleaking out, and to prevent air from leaking in.

The seal is mated to the transducer housing. The mating means may be anynumber of mechanical connections that allow for the air and water tightseal described above. Once the seal is in place, the cavity in thetransducer housing may be flooded with degassed water without waterescaping. The seal may also have an electronic or mechanical recognitiondevice such that the transducer housing will recognize the properplacement of the seal and move the ultrasound machine from a safe modeto an active mode. Furthermore an optical window may be placed either inthe membrane or in the retainer so that any kind of optical sensor orsafety device using an optical sensor may still detect the proper safetymaterial across the seal.

1. A disposable transducer seal comprising: a membrane beingsubstantially transparent to ultrasound energy, said membrane beingnon-porous to water and acoustic coupling fluids; a retainer having asubstantially annular configuration for holding said membrane; and ameans for mating said retainer with a transducer housing.
 2. The deviceof claim 1, wherein the membrane is a thermo-formable polyimide.
 3. Thedevice of claim 1, wherein the retainer further comprises an electronicrecognition device.